Effects of inert fillers on the mechanical and electrochemical properties of lithium salt-poly(ethylene oxide) polymer electrolytes

The effects of adding an inert filler (α-alumina) to lithium perchlorate-poly(ethylene oxide) polymer electrolytes have been investigated. It was found that additions of 10 vol. % α-alumina had a negligible effect on the ionic conductivity of the polymer but gave a significant improvement in the mechanical stability of the material at temperatures in excess of 100°C. A.C. measurements on samples containing 0 and 10 vol. % α-alumina gave values of 0.2 to 0.3 for the transport number of the lithium ions between 110 and 130°C.     

Thermal history — conductivity relationship in lithium salt-poly (ethylene oxide) complex polymer electrolytes

A.C. conductivity measurements on a number of lithium salt-poly(ethylene oxide) (PEO) complex polymer electrolytes have been correlated with the results of D.S.C. analysis. An enhancement in the conductivity of compositions with O:Li ratios of greater than 6:1 on annealing at above 150°C was attributed to the melting of the polymer crystalline phase and the retention of an amorphous polymer structure in the electrolyte on cooling down to the crystallisation temperature of the pure PEO phase.     

Stability domain of a complexed lithium salt-poly(ethylene oxide) polymer electrolyte

The redox stability domain of a polyethylene oxide-lithium trifluoromethanesulphonate polymer electrolyte has been investigated using low-sweep-rate voltammetry, in the range 100–170°C. Below 140°C, its voltage stability window is in excess of 3.3 volts, making it a candidate for use with practical electrochemical couples. The electrolyte is not, however, a pure cation conductor, and problems associated with the observed significant anion mobility must be overcome in order to improve the polymer's suitability as a solid-state electrolyte for battery applications.     

Characterization of poly(ethylene oxide) copper salt polymer electrolytes

The physico-chemical and electrochemical properties of a new class of polymer electrolytes formed by complexes of poly(ethylene oxide) and copper trifluorosulphonate salts have been investigated. The results suggest that these electrolytes are good copper ion conductors. Under particular conditions of concentration and temperature, and apparent electronic transport has also been evidenced.     

A phosphate additive for poly(ethylene oxide)-based gel polymer electrolytes

The influence of an organophosphosphate additive on poly(ethylene oxide) lithium bis(trifluoromethylsulfonyl)imide-based gel polymer electrolytes for secondary lithium battery applications is described. Tris(2-(2-methoxyethoxy)ethyl)phosphate, is compared to the well known gel-battery component, propylene carbonate, through a study of complex impedance analysis, differential scanning calorimetry, and limiting oxygen index combustion analysis. The conductivities of the gels at low concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (1.9–4.2 mol%) are higher to those of propylene carbonate-based systems with the same concentration. Despite micro-phase separation at high concentrations of tris(2-(2-methoxyethoxy)ethyl)phosphate (7.0–14.9 mol%), the conductivities remain comparable to systems that use propylene carbonate. The addition of tris(2-(2-methoxyethoxy)ethyl)phosphate to poly(ethylene oxide) gives increased fire retardance, while the addition of propylene carbonate to poly(ethylene oxide) results in increased flammability.     

Mixed solid electrolytes based on poly(ethylene oxide)

Polymer solid electrolytes from a PEO-NaI system were mixed with Nasicon and Al₂O₃ powders. As a result an increase of ionic conductivity exceeding 10^–1 S/cm at room temperature was observed for both cases. This increase was due to a higher concentration of amorphous phase which resulted apparently from a higher nucleation rate during the solidification process. The samples were studied using impedance spectroscopy, X-ray diffraction, electron microscopy, NMR, and other techniques.     

Ionic conductivity of electrolytes based on star-branched poly(ethylene oxide) with high concentration of lithium salts

Electrolytes based on star-branched poly(ethylene oxide) with lithium bis(trifluoromethanesulfone)imide LiTFSI and lithium iodide salts were prepared by casting from solution. The electrical properties of electrolytes subjected to various heating and cooling runs were studied by impedance spectroscopy and impedance spectroscopy simultaneous with optical microscope observation. Differential scanning calorimetry was used for additional characterization. The results indicate that in electrolytes with high content of salt, values of ionic conductivity comparable to that of dilute electrolytes can be achieved. Moreover, electrolytes with high amount of salt seem to show weaker temperature dependence of conductivity. Promising results in terms of ionic conductivity were obtained for mixture of LiTFSI and lithium iodide. A few problems which may decrease the performance of studied system as a solid electrolyte were also identified, from which changes of physical properties of samples subjected to thermal cycles and aging seem to be the most important ones.     

MgAl2SiO6-incorporated poly(ethylene oxide)-based electrolytes for all-solid-state lithium batteries

Poly(ethylene oxide) (PEO)-based composite polymer electrolytes (CPEs), comprising various concentrations of lithium hexafluorophosphate and magnesium aluminium silicate, were prepared by hot-press technique. The membranes were characterised by scanning electron microscopy, tensile and thermal analyses. It has been demonstrated that the incorporation of the ceramic filler in the polymeric matrix has significantly enhanced the ionic conductivity, thermal stability and mechanical integrity of the membrane. It also improved the interfacial properties with lithium electrode. Finally, an all-solid-state lithium cell composed of Li/CPE/LiFePO₄ has been assembled and its cycling performance was analysed at 70 °C. The cell delivered a discharge capacity of 115 mAh g^?1 at 1 °C rate and is found to be higher than previous reports.     

Solid polymer electrolytes based on poly(lithium carboxylate) salts

The ionic conductivity, lithium ion transference number, electrochemical stability, and thermal property of solid polymer electrolytes composed of poly(ethylene oxide) (PEO) and poly(lithium carboxylate)s, (poly(lithium acrylate) (Poly(Li-A)) or poly(lithium fumarate) (Poly(Li-F)), with and without BF₃·OEt₂ were investigated. The ionic conductivities of all solid polymer electrolytes were enhanced by one to two orders of magnitude with addition of BF₃·OEt₂ because the dissociation of lithium ion and carboxylate anion was promoted by the complexation with BF₃. The lithium ion transference number in the solid polymer electrolytes based on poly(lithium carboxylate)s showed relatively high values of 0.41–0.70, due to the suppression of the transport of counter anion by the use of a polymeric anion. The solid polymer electrolytes with addition of BF₃·OEt₂ showed good electrochemical stability.     

Poly(dimethylsiloxane)-poly(ethylene oxide) based polyurethane networks used as electrolytes in lithium electrochemical solid state batteries

Ionic conductivity and redox stability domain of a new type of polymer electrolyte have been studied. The polymer electrolytes were prepared from a network of poly (dimethylsiloxane-grafted ethylene oxide) copolymer crosslinked by an aliphatic isocyanate (grafted PDMS) and containing 10 wt% LiClO₄. Ionic conductivities higher than 10^?5 ω^?1 cm^?1 are obtained above 30°C. The study of the electrochemical stability of the crosslinking agent suggests that the unreacted isocyanate groups are not stable. The electroactivity domain of the grafted PDMS-LiClO₄ 10 wt% electrolyte is larger than 3 V. The performances of a solid state battery using this electrolyte have been investigated. The first discharge and charge depths were 73%. The rechargeability behaviour have been compared with those of a Li/RuO₂ battery with a linear high molecular weight P(EO)₈-LiClO₄ as electrolyte.     

Vibrational spectroscopy and structure of polymer electrolytes,poly(ethylene oxide) complexes of alkali metal salts

Complexes of poly(ethylene oxide) (PEO), with various alkali metal salts are known to exhibit ionic conductivities which exceed 10^?5(Ωcm)^?1 at moderate temperatures. We have employed IR and Raman spectroseopy to study well characterized samples of the following polymer-salt complexes: PEO·NaBr, PEO·NaI, PEO·NaSCN, PEO·NaBF₄, PEO·NaCF₃SO₃, PEO·KSCN, PEO·RbSCN and PEO·CsSCN. Cation-dependent vibrational bands observed in the far IR and M-O_n symmetric stretching bands observed in the Raman support a cation-oxygen atom interaction, and indicate the polyether chain may wrap around the cations. In particular, NaX and KX complexes of PEO are believed to have a helical configuration for the polymer which differs from that of pure PEO. Some general rules are presented for polymer-salt complex formation.     

Experimental investigations on poly(ethylene oxide) based sodium ion conducting composite polymer electrolytes dispersed with SnO2

New Na⁺ ion conducting composite polymer electrolytes comprising of polyethylene oxide (PEO)-NaClO₄ and PEO-NaI complexes dispersed with SnO₂ are reported. The results of the studies based on optical microscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infra-red (FTIR) spectroscopy, impedance analysis and mechanical testing are presented and discussed. The electrical conductivity of ≈5·10⁻⁵ S·cm⁻¹ at 40 °C was achieved for the dispersion of ≈10 wt.% of SnO₂ in both systems. The composition dependence of the conductivity has been well correlated with the variation in glass transition temperature and degree of crystallinity. A substantial enhancement in the mechanical properties of the composite films was observed at the cost of slight decrease in the conductivity at higher concentration of SnO₂. The temperature dependence of the conductivity follows apparently the Arrhenius type thermally activated process below and above the melting temperature of PEO. The conductivity of the materials has been found to be strongly humidity dependent. The materials are shown to be ionic with t_ion>0.9. The electrochemical stability of the materials has been observed to be up to ≈3.2 V for (PEO)₂₅NaClO₄+x% SnO₂ and is limited to ≈1.9 V for (PEO)₂₅NaI+x% SnO₂.     

Conductivity and dielectric relaxation of Li salt in poly(ethylene oxide) and epoxidized natural rubber polymer electrolytes

Two types of polymer electrolytes were studied: poly(ethylene oxide) (PEO) and epoxidized natural rubber (ENR) both filled with lithium perchlorate. Universal dielectric behavior and impedance relaxation were investigated at room temperature over a wide range of salt concentration. Complex impedance plots exhibit one semicircle in some cases (PEO polymer electrolytes) with an extended spike at low frequencies. This implies a double layer capacity strongly influences conductivity at low frequencies. In the ENR–salt system, semicircles can be obtained only at very high concentrations. This points towards stable resistor dominated networks only develop at very high salt concentrations for this system. Centers of the semicircles lie below real axis indicating non-Debye dielectric relaxation. The relaxation peak broadens and shifts to higher frequencies with increasing salt content. It indicates that the relaxation time of polarization relaxations decreases with ascending salt content. Relaxations occur at extremely low salt concentrations in PEO and only at very high salt concentrations in ENR. Hence, conductivity of ENR–salt is one to two orders of magnitude lower as for PEO–salt.     

Electrochemical and mechanical properties of nanochitin-incorporated PVDF-HFP-based polymer electrolytes for lithium batteries

Nanocomposite polymer electrolytes (NCPE) composed of poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) and chitin for different concentrations of LiClO₄ have been prepared by a hot-press technique. The prepared NCPE films were subjected to XRD, SEM, FTIR and tensile analyses. The thermal stability of NCPE membrane was investigated by TG-DTA. Ionic conductivity studies have also been made as a function of lithium salt concentration for different temperatures ranging from 0 to 80 °C. The polymeric membrane comprising PVDF-HFP/chitin/LiClO₄ of ratio 75:20:5 (wt.%) offered maximum ionic conductivity. Thermal study reveals that these membranes are stable up to 260 °C.     

Electrochemical studies on polymer electrolytes based on poly(methyl methacrylate)-grafted natural rubber for lithium polymer battery

MG30 is natural rubber grafted with 30% poly(methyl methacrylate). Gel polymer electrolytes containing MG30–LiCF₃SO₃–X (X = propylene carbonate, ethylene carbonate) are prepared by solution casting technique. The polymer–salt complexes were investigated using Fourier-transformed infrared. The ionic conductivity of the electrolytes are determined by the ac impedance studies over the temperature range of 303–383 K and is observed to obey the Vogel–Tamman–Fulcher (VTF) rule. The Li⁺ transference number obtained using the Bruce and Vincent method is <0.3. The Li/Li⁺ interface stability is established and the electrolytes were found to be able to withstand a voltage of more than 4.2 V.     

Polymer electrolytes based on poly(vinylidene fluoride-co-hexafluoropropylene) with crosslinked poly(ethylene glycol) for lithium batteries

The combination of a poly(ethylene glycol) (PEG) network and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) copolymer chains is one of the most efficient means for modifying PVDF-HFP gel electrolytes. Previous preparations tend to introduce contamination into the polymer gel electrolyte because of irradiation, high temperature or the initiator needed for crosslinking which might result in the electrochemical degradation. In order to overcome the above disadvantages, a new method has been developed to successfully prepare the semi-interpenetrating polymer networks of PVDF-HFP based electrolytes with crosslinked diepoxy polyethylene glycol (DIEPEG). In this process, impurities are avoided because of a moderate reaction temperature at 50 °C and poly(ethylenimine) (PEI) as the crosslinking agent. Microporous films with various compositions are prepared and characterized. Thermal, mechanical, swelling and electrochemical properties, as well as microstructures of the prepared polymer electrolytes have been investigated using thermogravimetric analysis, electrochemical impedance spectroscopy, linear sweep voltammetry, and scanning electron microscopy. The results show that the blend polymer electrolyte with PVDF-HFP/PEI + DIEPEG (60:40 w/w) has an ionic conductivity of 2.3 mS cm^? 1 at room temperature in the presence of 1 M LiPF₆ in EC and DMC (1:1 w/w). All the blend electrolytes are electrochemically stable up to 4.8 V versus Li/Li⁺. The results reveal that this new method may be very promising for improving PVDF-HFP based electrolytes.     

Solid state NMR study of sodium thiocyanate/poly(ethylene oxide) electrolytes

¹H-, ¹³C-, ²³Na-solid state NMR measurements have been used to characterise the morphology and the dynamics of several NaSCN-PEO mixtures. Selective ¹³C-MAS experiments allowed to determine the composition of the (PEO)_nNaSCN samples in terms of the different phases present, as well as the real stoichiometry of the crystalline complex. ¹H- and ¹³C-spin-lattice relaxation times provided estimates of the dimensions of the different domains and gave information on the dynamics of the polymer chains. ²³Na-MAS spectra and 2D nutation experiments allowed to individuate the presence of different environments for the sodium cations on the basis of their quadrupolar interactions.     

Conductivity studies of poly(ethylene oxide)(PEO)/poly(vinyl alcohol) (PVA) blend gel polymer electrolytes for dye-sensitized solar cells

Poly(ethylene oxide)(PEO)–poly(vinyl alcohol) (PVA) blend-based gel polymer electrolytes (GPEs) have been prepared by blending equal weights of PEO and PVA in ethylene carbonate (EC), dimethyl sulfoxide (DMSO), tetrabutylammonium iodide (TBAI), and iodine crystals (I₂). The conductivity, diffusion coefficient, number density, and ion mobility of the electrolytes have been calculated from the impedance data obtained from electrochemical impedance spectroscopy (EIS) measurements. The GPE with the composition of 7.02 wt%, PVA, 7.02 wt% PEO, 30.11 wt% ethylene carbonate (EC), 30.11 wt% DMSO, 24.08 wt% TBAI and 1.66 wt% I₂ exhibits the highest conductivity of 5.5 mS cm^?1 at room temperature. Dye-sensitized solar cells (DSSCs) with configuration fluorine tin oxide (FTO)/titanium dioxide/N3-dye/GPE/platinum/FTO have been fabricated and tested under the white light of intensity 100 mW cm^?2. The DSSC containing the highest conducting GPE exhibits the highest power conversion efficiency, η of 5.36 %.     

Ionic conductivity of LiX-oligo(ethylene oxide)-perfluoro polymer ternary hybrids

Polymeric solid electrolytes were prepared from inorganic lithium salts, endo-acetylated oligo(ethylene oxide) and polyanions with perfluoro(ethylene) main chain. High ionic conductivity was found when these ternary hybrids took micro-segregated structures with continuous cylindrical conduction columns of lithium salt-oligo(ethylene oxide) in the sea of perfluoro-poly(electrolytes). The ionic conductivity of more than 10^?5 S/cm was established at room temperature without affecting the processibility and flexibility of resulting hybrid films.     

Effect of fillers on magnesium–poly(ethylene oxide) solid polymer electrolyte

A solid polymer electrolyte (SPE) film consisting of poly(ethylene oxide) (PEO) with magnesium chloride as electrolytic salt and B₂O₃ as the filler has been prepared by solution casting technique. The polymeric film was flexible and self-standing with proper mechanical strength and studied for application in a solid-state rechargeable magnesium battery. The interactions between the filler and PEO chains are studied by differential scanning calorimeter and Fourier transform infrared techniques. Composition of SPE is optimized, and maximum conductivity is obtained at 2 wt% B₂O₃. Filler seems to increase the number of free magnesium cations by decoordinating the bond between magnesium cations and ether oxygen of PEO. Cyclic voltammetry results show the reversible capability of magnesium electrode. Solid-state magnesium cell employing magnesium anode, SPE, and manganese oxide was assembled, and its open circuit voltage is found to be 1.9 V.